The Vernier Three-Axis Magnetic Field Sensor: A Magic Wand for Magnets

What could be better than one anisotropic magnetoresistance magnetic field sensor? How about three anisotropic magnetoresistance magnetic field sensors and a Hall effect sensor as well! Pack them all into a lightweight watertight housing with a rechargeable battery and wired or wireless connectivity and you’ve got yourself a Vernier Three-Axis Magnetic Field Sensor.

Vernier Three-Axis Magnetic Field Sensor

Vernier Three-Axis Magnetic Field Sensor

I’ve been a fan of Vernier’s magnetic field sensors for decades, ever since the 1990s when my earth science students used the sensors with their primitive Apple laptops in the fields, hills, and caves of Craters of the Moon National Monument in Idaho. 

Back then the magnetic field sensor was long cabled tube with amplification box that connected to a computer via a wired and powered interface box of some variety (Bluetooth hadn’t yet cut it’s teeth in classroom electronics yet so adding “less” to wire was years away). Still, the students loved making sine waves of magnetic field strength within the futuristic Logger software. Measuring the earth’s magnetic field, as well as the orientation of two thousand-year old basalt flows. Students could pick up a broken piece of basalt and using the Vernier Magnetic Field Sensor re-orient the stone in relation to the larger background rocks.

In the classroom, the student used the Vernier Magnetic Field Sensor to locate and map magnetic objects buried in sand, and even hypothesize about the objects size, shape, depth, and density using a control set of objects and sandbox.

Today Vernier offers a wireless Three-Axis Magnetic Field Sensor as part of their Go Direct series of sensors. Back in the 1990s it was a substantial update when the DIN connector changed to a BTA connector, and the beige serial connection box morphed into the translucent LabPro. To think that a couple blinking lights was exciting feedback from a battery-powered interface! 

Go Direct sensors are a new class of Vernier probeware that evolved out of almost 40 years of science teaching hardware and software that built in or bolted on advancements in consumer technology including replaceable battery power, USB connectors, rechargeable batteries, mobile device compatibility, touch screens, multiple inputs, online support, digital curriculum, wireless communications, more touch screens, low energy Bluetooth, and now universal power and data connectivity using the EPS standard.

Today’s topic is the Go Direct Vernier Three-Axis Magnetic Field Sensor. The sensor is a breakthrough in capability, size, weight, price, and most important performance. The Vernier Three-Axis Magnetic Field Sensor measures magnetic field strength along three planes within one sensor. The 12.2 centimeter long probe (19 cm overall) has a tiny 0.7 cm footprint on the tip allowing the probe’s proboscis to be inserted inside some small spaces such as inside solenoids with no clumsy cables, or probe rotations to mimic three-axis measurements.

But should the need for a cabled connection between Go Direct sensor and digital device, that is certainly possible as well. Using the same micro-USB port that charges the internal battery, the Go Direct sensor can be hard-plugged directly into a computer. Why go wired when you could be wireless? Good question. The backwards compatibility allowing a copper connection over an electromagnetic one expands the usability of the sensor. A little-discussed element in the science lab is sacrificial computer or tablet. As technology ages, it looses it reliability, connectivity and security. By being able to buy the most modern digital sensor yet plug it into an obsolete machine for lab work fresh life is breathed  into old tech. The Go Direct concept is also a significant upgrade when using BYOD (Bring Your Own Device) science classes because an old Windows machine will work along side a Macbook Pro next to a Chromebook, next to an iPad, next to an iPhone or Android smartphone.

But on to the Vernier Three-Axis Magnetic Field Sensor. By using multiple sensors built into a single  33 gram probe, the nimble Vernier Three-Axis Magnetic Field Sensor can be waved  about like a magic wand, or maybe more like a symphony conductor’s baton as the student conducts their experiments. And at only 33 grams, that almost 14 Vernier Three-Axis Magnetic Field Sensors per pound.


So how does the sensor work? It uses two methods of measuring magnetic fields. The tip of the sensor has a +/- 5 mT chip that applies the property William Thompson (aka Lord Kelvin) observed in 1856, a phenomenon now called anisotropic magnetoresistance or AMR.

So what do you get when you mix the quantum physics effects of spin-orbit interaction with the magnetization of a material? Magic? Well actually anisotropic magnetoresistance. But it seems like magic. Ever wonder how a digital compass works? Like the kind in cell phone apps and GPS receivers. Do you think there’s a little magnet spinning in your phone? Actually, there might be, but not for the compass. Moving metal in a phone is how it vibrates when a call or text comes in. In the case of anisotropic magnetoresistance, there is an effect on electrical resistance between the direction of magnetization and its angle relative to an electrical current. Maximum electrical resistance occurs when the magnetic field is parallel to the direction of the electrical current. And of course the sensor must be calibrated for the job it will do.

In order to determine polarity of the magnetic field, a thin film of permalloy has strips of gold (or aluminum) laid across it inclined at forty-five degrees. With the current unable to flow along the normal path of least resistance, instead it is offset at and angle and thus forcing it to have a dependance around a neutral point. Like I said, magic.

Back in 1960 at the General Conference on Weights and Measures, the unit of Tesla was announced. One tesla is equal to one weber per square meter with the weber (Wb) being the SI unit of magnetic flux. The weber is named after the German physicist Wilhelm Eduard Weber. 

Measuring the X-direction Magnetic Field Magnetic fields that point in the same direction the wand is pointing are recorded as positive, and fields that point in the opposite direction are recorded as negative. Thus, the magnetic field of the Earth will register as a positive field when the wand is pointed toward the magnetic pole in the Earth’s northern hemisphere, which is a South magnetic pole. When the wand is aligned with a permanent magnet and pointed toward the South pole of a magnet it will also record a positive field.

Measuring y- and/or z-directions The marks on the sides of the wand, at the tip, indicate the y- and z-directions of positive magnetic field measurements, as well as marking the location within the housing where the ±5 mT magnetic field sensor is located. This is important for consistent placing of the sensor and accurately measuring the distance between the sensor and the source of a magnetic field.

 

In the case of the Vernier Three-Axis Magnetic Field Sensor measurements of +/-5 mT are possible as well as measurements of +/-130 mT. How can this be, you might ask, with no switch between a high and low setting like on previous magnetic field sensors? Great question. Part of the magic of this sensor is that it is actually multiple sensors. About five millimeters from the tip of the sensor is the +/-5 mT anisotropic magnetoresistance sensor, and about 10.5mm from the tip is the +/-130 mT Hall effect sensor.

The tip of the sensor is noted with three embossed dots indicating the actual location of the sensors with two labeled as Y and Z with the third dot on the very end of the probe completing the triple capabilities of the Go Direct Vernier Three-Axis Magnetic Field Sensor

Just upstream a centimeter on the probe’s shaft is a Hall effect sensor for measuring a larger amount of magnetic flux. The Hall effect is the production of a voltage difference across an electrical conductor but transverse to an electric current in the conductor and to a magnetic field perpendicular to the current. Edwin Hall discovered the effect in 1879 while working on his doctoral degree at Johns Hopkins University. If only we could all be so lucky. And Hall did all this work almost two decades before the electron was even discovered!

At total of six data channels are measurable with the Go Direct Vernier Three-Axis Magnetic Field Sensor: X, Y, and Z magnetic field, and X, Y, and Z 130 mT magnetic field.

The durable sensor is water resistant, but the ~2.4 GHz of the Bluetooth signal is not. So underwater measurements would be a good candidate for using a USB wire.

The software to make the Vernier Three-Axis Magnetic Field Sensor really go to work is called Graphical Analysis 4.  So powerful is GA4 that it will get its own writeup in the future. But don’t wait for that day. Download it for free now.

For when you want to hold the Vernier Three-Axis Magnetic Field Sensor stationary, there are many solutions. No tripod mount is on the sensor, but the sensor fits wonderfully in the Joby GripTight ONE Mount which then can be attached to a tripod. Of course you could also just use a rubber band.

Conducting experiments and inspections with magnets is as easy as waving your magic wand. Don’t have a magic wand? Then use the next best thing, a Go Direct Vernier Three-Axis Magnetic Field Sensor.

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